a. The Field of the Invention
This invention is related with the art of providing and making use of respirators, that is systems and devices designed for pulsingly and forcibly introducing under appropriately slight but positive pressure through a face mask, tracheal tube or the like metered amounts of gaseous mixture into the respiratory system of a patient to expand the lungs in simulation of the normal inhalation portion of the respiratory cycle.
More particularly this invention is concerned with a new and improved respirator device of the type including a variable volume chamber having an at least partly pliable wall and confined within an enclosure having essentially rigid or unextensible walls, the space or volume internal to said variable volume chamber being connected, in operation of the device and by means of couplings, duct means and suitable check valves, with a source of slightly pressurized gaseous mixture and respectively with the patient's respiratory system.
The said variable volume chamber acts as a reciprocating pump and it is actuated by alternately applying a superatmospheric and a subatmospheric fluid generally air pressure in the interspace existing between the unextensible walls of the enclosure and the pliable wall of said chamber.
B. The Prior Art
This art is a widely known and well worked one and a variety of apparatuses for the control of respiration, resuscitation and anaesthesia have been proposed, manufactured and currently made use of. The gaseous mixture to be applied to a patient who is unable to perform satisfactory respiration without external assistance may be fresh air or oxygen enriched air as well as anesthetic or other agent containing mixture. The selection of the particular gas or mixture, of the rate, frequency and other flow parameters, and of the procedure of supplying same is the province of the physician's determination. For the purposes of this specification and in the claims, the terms "gas", "gaseous mixture" and also "gaseous volumes" will therefore be understood to mean any gaseous fluid and fluid amounts such as prescribed by the physician, together with the parameters of the respiratory pattern.
According to current art the outlet of the respirator, from which the gaseous mixture is caused to pulsingly issue, is connected to the face mask, tracheal tube or the like, by means of a tubular duct or hose, generally made of a rubbery or other pliable material, of such length to easily cover the interval between the respirator and the patient, who is sometimes enclosed into a confined thermally and atmospherically conditioned environment. Such tubular duct has a cross-sectional area such to ensure an undisturbed flow at the desired rate, without undue pressure drop. The inner volume of said duct means is therefore rather relevant and the gaseous mixture confined thereinto, at the end of any inhalation step, will be compressed but not actually supplied in the lungs of the patient. Such inner volume is generally termed "compressible volume, or space".
From the point of view of properly transferring into the patient's respiratory system the gaseous volumes for which the respirator has been adjusted, without unduly effecting the pressure, this compressible volume is a parasitic one and prejudices the correct volumetrical supplying of the prescribed gaseous volumes. The said compressible volume confined within the duct means of conventional assemblies is relevant and its measure can be of the order of one liter (dm.sup.3) or more.
These noticeably large compressible volumes can be tolerated in the general case of treatment of grown-up patients and generally when substantial volumes are supplied at any breathing cycle, the prejudice of the correct supplying being a function of the ratio of the gaseous volume as a whole relatively to the compressible volume. In the field of paediatrics, and most particularly when the breathing cycle of prematurely born babies is to be ensured, the compressible volume leads to very serious problems, taking into account that the tiny respiratory systems of such patients can inhale gaseous volumes to be measured in terms of cubic centimeters. Such problems are well known to physicians and paediatrists, and to provide shorter and smaller hoses or duct means is a known expedient for decreasing the compressible volume. Such dimensional limitation of the duct means cannot however provide a completely satisfying operation, for evident reasons, in particular by the fact that the apparatus cannot be placed too close to the patient.
It is therefore a principal object of this invention to provide a new and advantageous respirator system which is not subject to the above and other limitations. More specifically, it is an object of this invention to provide a new respirator device of the type referred to above, so designed that the above discussed compressible volume will be essentially zeroed, while the source of the gaseous mixture and that of the pulsing fluid pressure can be located at a safe, substantial and undisturbing distance from the patient. The system and the device of the invention are particularly but not exclusively advantageous in the field of paediatrics, as it will be readily apparent as this description proceeds.